SCIENCE CHINA Technological Sciences © Science China Press and Springer-Verlag Berlin Heidelberg 2015 tech.scichina.com link.springer.com *Corresponding author (email: zzhao@sjtu.edu.cn)  Article  March 2015 Vol.58 No.3: 1–9 doi: 10.1007/s11431-015-5772-9 Experimental and numerical investigation of failure mode in geometrically imperfect DP590 steel ZHUANG XinCun, XU Cheng & ZHAO Zhen * Institute of Forming Technology & Equipment, School of Materials Science and Engineering, Shanghai Jiaotong University, Shanghai 200030, China Received November 3, 2014; accepted January 6, 2015 Various microstructure-level finite element models were generated according to the real microstructure of DP590 steel to cap- ture the mechanical behavior and fracture mode. The failure mode of the dual-phase (DP) steels, mainly resulting from micro- structure-level inhomogeneity and initial geometrical imperfection, was predicted using the plastic strain localization theory. In addition, dog-bone-type tensile test specimens with different edge qualities were prepared and the deformation processes were recorded using a digital image correlation system. When the steel exhibited no initial geometrical imperfection, void initiation was triggered by decohesion between martensite and ferrite which was predicted based on the severe strain concentration, or tensile stress in areas where stress triaxiality and strain values were high. Final failure was caused by shear localization in the vicinity. Moreover, the initial geometrical imperfections severely affected the overall ductility and failure mode of the DP590 steel. When initial geometrical imperfections were deeply ingrained, an incipient crack began at the site of initial geometrical imperfection, and then caused progressive damage throughout the microstructure, from the area of shear localization to the fi- nal fracture. Overall, the depth of the geometrical imperfection was the critical factor in determining whether internal decohe- sion or a local crack plays a dominant role. representative volume element, dual-phase (DP) steel, geometrical imperfection, failure mode Citation: Zhuang X C, Xu C, Zhao Z. Experimental and numerical investigation of failure mode in geometrically imperfect DP590 steel. Sci China Tech Sci, 2015, 58, doi: 10.1007/s11431-015-5772-9 1 Introduction In the modern automotive industry, automobile body weight has been increasingly reduced by implementing new mate- rial-processing technologies and lightweight materials. The dual-phase (DP) steels with a microstructure consisting of a ferrite matrix, in which particles of martensite are dispersed, have received a substantial amount of attention because they are of high strength and feature a high work-hardening rate and ductility [1,2]. Therefore, they are suitable for use in the sheet metal forming processes. However, the DP steels eas- ily develop edge cracks that complicate describing the fail- ure mode and predicting ductility during post-processing operations conducted using conventional procedures such as the forming limit diagram. To investigate edge cracks, Sartkulvanich et al. [3] fo- cused on numerical modeling and experimented with the blanking and hole expansion of DP590 steel, characterizing the edge quality of various die clearances and demonstrating the effect that a sheared edge exerts on stretchability. Konieczny and Henderson [4] presented sheared-edge fail- ure modes for advanced high strength steel (AHSS) sub- jecting to various loading modes, and discussed the influ- ence of blanking clearance and edge morphology parame- ters on formability. Based on the experimental data, they doi: 10.1007/s11431-015-5772-9